Trump makes 'robo-call' for Roy Moore

President Donald Trump has sought to boost Republican US Senate candidate Roy Moore by releasing a recorded phone call on his behalf in the final stretch of a bitter Alabama election marked by accusations of sexual misconduct against Moore.

Moore, 70, a conservative Christian and former Alabama Supreme Court justice, will face off in Tuesday's election against Democrat Doug Jones, 63, a former US attorney.

On Monday, the eve of the election, the Moore campaign is rolling out a "robo-call" with Trump's voice telling voters that if they do not support the Republican candidate, progress on his agenda will be "stopped cold".

Democrats then decided to make robo-calls using two of their party's own big guns - former president Barack Obama and vice president Joe Biden.

The race has divided Trump's Republican Party and given Democrats a rare opening in deeply conservative Alabama, which has sent only Republicans to the US Senate for the past 20 years.

A Fox News Poll conducted on Thursday and released on Monday put Jones ahead of Moore, with Jones potentially taking 50 per cent of the vote and Moore 40 per cent. Fox said 8 per cent of voters were undecided and 2 per cent support another candidate.

Moore has maintained a low profile, refusing interview requests and holding few public events.

He planned an election-eve rally with former White House strategist Steve Bannon, an executive at the right-wing Breitbart News site who has been one of Moore's most ardent backers.

While Trump, who swept Alabama in the 2016 presidential election, backs Moore, many other national Republicans, such as Senate majority leader Mitch McConnell, have distanced themselves after Moore was accused last month by several women of pursuing them when they were teenagers and he was in his 30s.

The allegations have given new hope to Jones, who has touted a record that includes prosecuting former Ku Klux Klan members responsible for a 1963 bombing of a black church in which four girls were killed.

If Jones wins on Tuesday, Republicans would control the Senate by a slim 51-49 margin, giving Democrats much-needed momentum ahead of the November 2018 congressional elections, when control of both chambers of congress will be at stake.

Jones has spent the past week rallying African-Americans, the most reliably Democratic voters in the state, and hammering Moore in television ads.

He held a series of get-out-the-vote rallies across the state on Sunday.